Topic 11 - Nuclear Radiation

Question 1

What is the formula for the background count rate?

Answer 1

Background Count Rate = Total Background Counts / Time

Units: counts per second (cps) or counts per minute (cpm)

Question 2

Use the binding energy per nucleon curve to explain how fusion and fission both release energy. (3 marks)

Answer 2

• Fusion involves an increase in the binding energy (per nucleon) as the number of nucleons increases
• Fission involves an increase in the binding energy (per nucleon) as the number of nucleons decreases
• If binding energy per nucleon increases, energy is released in the process

Question 3

State what is meant by binding energy. (2 marks)

Answer 3

• The energy equivalent to the mass deficit
• When nucleons bind together to form an atomic nucleus

Question 4

The energy radiated by stars is released by nuclear fusion.

Explain the conditions required to bring about and maintain nuclear fusion in stars.
(6 marks)

Answer 4

• Requires a (very) high temperature
• Nuclei all have a positive charge leading to a large repulsive force between nuclei
• At high temperatures nuclei have high kinetic energy, sufficient to overcome repulsion
• Nuclei must get close enough to fuse
• Requires (very) high density
• Collision rate must be high enough to sustain fusion

Question 5

A teacher tested an unknown radioactive source. He set up the source and a GM tube, as shown.

The initial count rate is determined without an absorber between the GM tube and
the source.

When an aluminium sheet of thickness 0.5cm was placed between the source and the GM tube, the count rate decreased to background level.

The teacher then removed the aluminium sheet and replaced it with a sheet of paper. There was no change in the initial count rate.

Explain which type of radiation is emitted from the source.

You should refer to the penetration of each type of radiation through each sheet of absorber. (4 marks)

Answer 5

• Alpha radiation would not pass through the sheet of paper
• No change in count rate when paper placed (between source and GM tube), so there can’t be any alpha radiation
• There can’t be any gamma radiation, as gamma radiation would pass
  through the aluminium sheet
• It must be beta radiation as beta radiation would not pass through the
  aluminium sheet.